Solid-state imaging device, method for manufacturing solid-state imaging device, and imaging apparatus

ABSTRACT

A solid-state imaging device includes a first electrode, a second electrode disposed opposing to the first electrode, and a photoelectric conversion layer, which is disposed between the first electrode and the second electrode and in which narrow gap semiconductor quantum dots are dispersed in a conductive layer, wherein one electrode of the first electrode and the second electrode is formed from a transparent electrode and the other electrode is formed from a metal electrode or a transparent electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device, a methodfor manufacturing the solid-state imaging device, and an imagingapparatus.

2. Description of the Related Art

Along with an increase in the number of pixels of a solid-state imagingdevice (image sensor), a size reduction of a pixel has been developed.

On the other hand, an improvement of moving image characteristicsthrough high-speed imaging has been developed at the same time.

In the case where the pixel is miniaturized and high-speed imaging isconducted, the number of photons incident on one pixel decreases anddesensitization occurs.

Furthermore, regarding a surveillance camera, there is a demand for acamera suitable for photographing in a dark place. Here, ahigh-sensitivity sensor is desired.

One example of attempts to enhance sensitivity is signal amplificationthrough avalanche multiplication.

For example, there is an attempt to effect avalanche multiplication ofphotons through application of a high voltage (refer to IEEETransactions Electron Devices Vol. 44, NO. 10, October, 1997, forexample). Here, since a high voltage of 40 V is applied to effectavalanche multiplication, it is difficult to make a pixel finer becauseof a crosstalk problem and the like. In the case of this sensor, thepixel size is 11.5 μm×13.5 μm.

Moreover, another avalanche multiplication type image sensor has beendisclosed (refer to IEEE J. Solid-State Circuits, 40, p. 1847, 2005, forexample). Regarding this avalanche multiplication type image sensor, itis desired to apply a voltage of 25.5 V to effect avalanchemultiplication. Therefore, in order to avoid crosstalk, a wideguard-ring layer or the like is necessary, and a large pixel size of 58μm×58 μm is desired.

In this regard, not only the above-described problem in that a highdrive voltage is desired to effect avalanche multiplication forenhancing the sensitivity, but also a photon shot noise problem occursat the same time because of a reduction in the number of photons. Thatis, since the photon is a Bose particle, overlapping of particlesoccurs, and in the continuous light, there are parts, in which photonsare dense, and parts, in which photons are sparse (photon bunchingeffect). The noise Nn due to this fluctuation is the square root of thenumber of photons Ns as represented by the following equation.Nn=√Ns

Therefore, the SN ratio becomes Ns/Nn (=√NS), and as the number ofphotons Ns decreases, the SN ratio decreases at the same time.

This refers to that a proportion of the photon shot noise relative tothe signal increases.

In such a case, not only the signal, but also the photon shot noise isamplified at the same time through avalanche multiplication.Consequently, if multiplication is effected while the proportion of thephoton shot noise is large, that is, the SN ratio is low, the noisebecomes large relatively and the image quality deterioratessignificantly.

SUMMARY OF THE INVENTION

The present inventor has recognized that the photon shot noise isamplified together with the signal at the same time through avalanchemultiplication.

It is desirable to enhance the sensitivity through avalanchemultiplication while photon shot noise is suppressed.

A solid-state imaging device according to an embodiment of the presentinvention includes a first electrode, a second electrode disposedopposing to the above-described first electrode, and a photoelectricconversion layer, which is disposed between the above-described firstelectrode and the above-described second electrode and in which narrowgap semiconductor quantum dots are dispersed in a conductive layer,wherein one electrode of the above-described first electrode and theabove-described second electrode is formed from a transparent electrodeand the other electrode is formed from a metal electrode or atransparent electrode.

Since the solid-state imaging device according to an embodiment of thepresent invention includes the photoelectric conversion layer, in whichnarrow gap semiconductor quantum dots are dispersed in the conductivelayer, avalanche multiplication can be effected by low voltage drive.

A method for manufacturing a solid-state imaging device, according to anembodiment of the present invention, includes the steps of forming acharge accumulation layer on a silicon substrate, forming a pixelelectrode on the above-described charge accumulation layer, forming aninsulating film covering the above-described pixel electrode, forming aplug, which is connected to the above-described pixel electrode, in theabove-described insulating film, forming a first electrode, which isconnected to the above-described plug, on the above-described insulatingfilm, forming a conductive layer, in which narrow gap semiconductorquantum dots are dispersed, on the above-described first electrode, soas to form a photoelectric conversion layer, and forming a secondelectrode on the above-described photoelectric conversion layer, whereinone electrode of the above-described first electrode and theabove-described second electrode is formed from a transparent electrodeand the other electrode is formed from a metal electrode or atransparent electrode.

In the method for manufacturing a solid-state imaging device, accordingto an embodiment of the present invention, the photoelectric conversionlayer is formed by forming the conductive layer, in which narrow gapsemiconductor quantum dot are dispersed. Therefore, avalanchemultiplication can be effected by low voltage drive.

An imaging apparatus according to an embodiment of the present inventionincludes a light-condensing portion to condense incident light, animaging portion including a solid-state imaging device to receive andphotoelectrically convert the light condensed with the above-describedlight-condensing portion, and a signal processing portion to process thesignal subjected to the photoelectrical conversion, wherein theabove-described solid-state imaging device includes a first electrode, asecond electrode disposed opposing to the above-described firstelectrode, and a photoelectric conversion layer, which is disposedbetween the above-described first electrode and the above-describedsecond electrode and in which narrow gap semiconductor quantum dots aredispersed in a conductive layer, while one electrode of theabove-described first electrode and the above-described second electrodeis formed from a transparent electrode and the other electrode is formedfrom a metal electrode or a transparent electrode.

In the imaging apparatus according to an embodiment of the presentinvention, the solid-state imaging device including the photoelectricconversion layer, in which narrow gap semiconductor quantum dots aredispersed in the conductive layer, is used in the imaging portion.Therefore, avalanche multiplication can be effected by low voltagedrive.

Regarding the solid-state imaging device according to an embodiment ofthe present invention, avalanche multiplication can be effected by lowvoltage drive. Therefore there is an advantage that the sensitivity ofeven a fine pixel can be enhanced through multiplication.

In the method for manufacturing a solid-state imaging device, accordingto an embodiment of the present invention, the photoelectric conversionlayer, in which narrow gap semiconductor quantum dots are dispersed inthe conductive layer, is formed. Therefore, avalanche multiplication canbe effected by low voltage drive, and there is an advantage that asolid-state imaging device, in which the sensitivity of the fine pixelis enhanced, can be produced.

The imaging apparatus according to an embodiment of the presentinvention includes the high-sensitivity solid-state imaging device.Therefore, imaging can be conducted with high sensitivity. Consequently,there is an advantage that photographing can be conducted with highimage quality even in a dark photographing environment, for example, innight photographing, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration sectional view showing a firstexample of a solid-state imaging device according to a first embodimentof the present invention;

FIG. 2 is a band diagram for explaining avalanche multiplication;

FIG. 3 is a schematic configuration sectional view showing a diffusioncurrent in a lateral direction in the configuration, in which acondenser lens is not disposed;

FIG. 4 is a schematic configuration sectional view showing a diffusioncurrent in a lateral direction in the configuration, in which acondenser lens is disposed;

FIG. 5 is a diagram showing the results of simulation of a diffusioncurrent in a lateral direction depending on presence or absence of acondenser lens;

FIG. 6 is a circuit diagram showing an example of a reading circuit;

FIG. 7 is a band diagram at zero bias with respect to a solid-stateimaging device 1;

FIG. 8 is a band diagram at reverse bias with respect to the solid-stateimaging device 1;

FIG. 9 is a band diagram at zero bias with respect to the solid-stateimaging device 1;

FIG. 10 is a band diagram at reverse bias with respect to thesolid-state imaging device 1;

FIG. 11 is a diagram for explaining photon shot noises of a solid-stateimaging device (image sensor);

FIG. 12 is a schematic configuration sectional view showing a secondexample of a solid-state imaging device according to a second embodimentof the present invention;

FIG. 13 is a diagram showing the relationship between the number ofincident photons exhibiting temporal fluctuations in the number ofphotons and the time of a solid-state imaging device 2;

FIG. 14 is a diagram showing the relationship between the amount ofphotons and the time based on a simulation;

FIG. 15 is a diagram showing the relationship between the emissionintensity and the time;

FIG. 16 is a schematic configuration sectional view showing a modifiedexample 2 of the second example of the solid-state imaging deviceaccording to the second embodiment of the present invention;

FIG. 17 is a circuit block diagram showing a CMOS image sensor, to whicha solid-state imaging device is applied;

FIG. 18 is a band diagram with respect to the solid-state imaging device1;

FIG. 19 is a circuit block diagram showing a CCD, to which a solid-stateimaging device is applied;

FIG. 20 is a schematic configuration diagram showing an example of adipping method for forming a photoelectric conversion layer; and

FIG. 21 is a block diagram showing an imaging apparatus according to anembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments (hereafter referred to as embodiment) forexecuting the present invention will be described below.

1. First Embodiment Configuration of First Example of Solid-StateImaging Device

A first example of the configuration of a solid-state imaging deviceaccording to a first embodiment of the present invention will bedescribed with reference to a schematic configuration sectional viewshown in FIG. 1.

As shown in FIG. 1, for example, a p-type silicon substrate is used as asilicon substrate 11. A plurality of pixels are disposed on theabove-described silicon substrate 11. In the drawing, two pixels areshown as typical examples.

A charge accumulation layer 12 is disposed on the above-describedsilicon substrate 11 on a pixel basis. This charge accumulation layer 12is formed from, for example, an n-type impurity diffusion layer. Forexample, the silicon substrate 11 is doped with an n-type impurity,e.g., phosphorus (P) or arsenic (As), so as to form the chargeaccumulation layer 12.

Pixel electrode 13 is disposed on the above-described chargeaccumulation layer 12. Furthermore, a gate MOS 14 to read a signal fromthe charge accumulation layer 12 to a reading circuit (not shown in thedrawing) is disposed, on a pixel basis, on the above-described siliconsubstrate 11. In this gate MOS 14, a gate electrode 14-2 is disposed onthe silicon substrate 11 with a gate insulating film 14-1 therebetween.

An insulating film 15 covering the above-described pixel electrodes 13,the gate MOSs 14, and the like is disposed on the above-describedsilicon substrate 11. This insulating film 15 is formed from, forexample, a silicon oxide film. As a matter of course, the insulatingfilm 15 may be formed from an inorganic insulating film or an organicinsulating film other than the silicon oxide film.

Plugs 16 connected to the above-described pixel electrodes 13 aredisposed in the above-described insulating film 15. This plug 16 isformed from, for example, tungsten. As a matter of course, electricallyconductive materials other than tungsten can be used.

First electrodes 21 connected to the above-described plugs 16 aredisposed on the above-described insulating film 15. These firstelectrodes 21 are disposed separately on a pixel basis. This electrodeis formed from a transparent electrode material of, for example, indiumtin oxide (ITO), indium zinc oxide, or zinc oxide. Alternatively, thiselectrode is formed from a metal electrode of lithium fluoride (LiF),calcium, or the like. That is, it is preferable that the metal electrodeof the first electrode 21 has a work function smaller than the workfunction of a conductive layer 22 and the Fermi level of the metalelectrode of the first electrode 21 is higher than the HOMO level (orthe energy level of a valence band) of the conductive layer 22.

A photoelectric conversion layer 24, in which narrow gap semiconductorquantum dots 23 are dispersed in a conductive layer 22, is disposed onthe above-described first electrodes 21.

The narrow gap semiconductor quantum dot 23 is formed in such a way thatthe band gap is 1 eV or less and the particle diameter is, for example,10 nm or less. Examples of materials therefor include a lead seleniumcompound (PbSe), a lead sulfur compound (PbS), a lead tellurium compound(PbTe), a cadmium selenium compound (CdSe), a cadmium tellurium compound(CdTe), an indium antimony compound (InSb), and an indium arseniccompound (InAs).

Furthermore, as for the above-described conductive layer 22,poly2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (hereafterabbreviated as MEH-PPV) is used.

A second electrode 25 is disposed on the above-described photoelectricconversion layer 24. This second electrode 25 is an electrode on thelight-incident side and, therefore, is formed from a transparentelectrode of, for example, indium tin oxide (ITO), indium zinc oxide, orzinc oxide, which has a light-transmitting property.

Moreover, color filter layers 31 are disposed on the above-describedsecond electrode 25. In this regard, a transparent insulating film (notshown in the drawing) may be disposed as a base material of the colorfilter layers 31.

In addition, a condenser lens 33 is disposed, on a pixel basis, on theabove-described color filter layer 31.

The solid-state imaging device 1 has the above-described configuration.

Explanation of Avalanche Multiplication of Solid-State Imaging Device

Next, the principle of avalanche multiplication will be described below.

The avalanche multiplication refers to that in the case where anelectron or a hole is accelerated and collides with a crystal atom,kinetic energy is given to the crystal, an electron present in a valenceband is excited to a conduction band by the given energy and, thereby, afresh electron-hole pair is yielded. The multiplication occurssignificantly by repeating this process.

The above-described solid-state imaging device 1 includes thephotoelectric conversion layer 24, in which narrow gap semiconductorquantum dots 23 are dispersed in the conductive layer 22. Therefore,carriers generated through photoelectric conversion are transported inthe electrically conductive photoelectric conversion layer 24.Consequently, a multiplication function is performed and the avalanchemultiplication can be effected by low voltage drive. Hence, there is anadvantage that the sensitivity of even a fine pixel can be enhancedthrough multiplication.

The reason for a high drive voltage of an avalanche multiplication typesolid-state imaging device (image sensor) is that a high electric fieldis necessary to accelerate electrons or holes generated throughphotoelectric conversion and, consequently, it is necessary to apply ahigh voltage.

Therefore, in order to reduce the drive voltage, it is desirable to givethe kinetic energy to the electrons or the holes generated throughphotoelectric conversion by another method.

According to a document “PHYSICAL REVIEW LETTERS Vol. 92, Num. 18,186601 (2004)”, as shown in FIG. 2, when light is applied to a narrowgap semiconductor quantum dot, an electron-hole pair is yielded throughphotoelectric conversion. In the drawing, hv represents light energy, e⁻represents an electron, h⁺ represents a hole, and E_(gap) representsband gap energy.

At this time, in the case where the condition,(photon energy of incident light)>(band gap of quantum dot),is satisfied, the electron-hole pair has excess kinetic energy. Thisexcess energy is represented by(excess kinetic energy)=(photon energy of incident light)−(band gap ofquantum dot).

If this excess kinetic energy is larger than the band gap of quantumdot, an electron present in the valence band is excited again to theconduction band through the collision process and, thereby, anotherfresh electron-hole pair is yielded. If the excess kinetic energy is mtimes the band gap of quantum dot or more (where m represents a naturalnumber), that is, the condition,(excess kinetic energy)≧m×(band gap of quantum dot),is satisfied, at least m times of multiplication occurs by the photonenergy alone.

In the range of the wavelength of the visible light of 400 nm to 650 nm,the photon energy is within the range of 1.9 eV to 3.1 eV. Here, forexample, if a narrow gap semiconductor quantum dot of PbSe (band gapenergy: Eg=0.3 eV) is used for photoelectric conversion, 6 times to 10times of multiplication is possible. As for this multiplication, it isindicated that electric field is not substantially necessary.

Furthermore, besides PbSe described above, multiplication similar tothat in the case of PbSe is effected effectively with respect to PbS,PbTe, CdSe, CdTe, InSb, InAs, and the like, which have a band gap of 1eV or less, as described above.

That is, the above-described solid-state imaging device 1 enables toproduce a high-sensitivity sensor compatible with a fine pixel throughavalanche multiplication effected by low-voltage drive by application ofthe above-described avalanche multiplication principle.

Explanation of Current Diffusion of Solid-State Imaging Device

As is described above with reference to FIG. 1, the narrow gapsemiconductor quantum dots 23 having particle diameters of 10 nm or lessare dispersed in the conductive layer 22 constituting the photoelectricconversion layer 24.

The above-described conductive layer 22 may be formed from an organicelectrically conductive polymer material or an electrically conductivelow molecular material. Alternatively, inorganic materials havingelectrical conductivity may be used.

Furthermore, the conductive layer 22, in which the narrow gapsemiconductor quantum dots 23 are dispersed, is sandwiched between thesecond electrode 25, which is a transparent electrode disposed on thelight-incident side, and the first electrodes 21 (metal electrodes ortransparent electrodes), which are disposed on the side opposite to thelight-incident side and which are separated on a pixel basis.

In order to improve the incident efficiency of light and ensure a largeopening, a plug 16 is disposed as described above and, thereby, theabove-described first electrode 21 is brought into the state of beinglifted to a higher level apart from the reading circuit portion of thegate MOS or the like, and the photoelectric conversion layer 24 isdisposed all over the surface above the substrate.

The second electrode 25 on the light-incident side is to avoid chargingof holes and, therefore, is not necessarily separated on a pixel basis,although may be separated.

Color filter layers 31 for dispersion are disposed on the individualpixels above the above-described second electrode 25.

Here, the conductive layer 22 may be separated on a pixel basis throughetching or the like in order to suppress diffusion of the current in alateral direction. Furthermore, as shown in FIG. 1 described above,light may be condensed on the vicinity of the center of the pixel bydisposing the condenser lens 33 as the uppermost portion of each pixeland mainly undergo photoelectric conversion there, so as to suppressdiffusion current in the lateral direction.

That is, as shown in FIG. 3, in the configuration, in which a condenserlens is not disposed, the light enters the photoelectric conversionlayer 24 uniformly so as to undergo photoelectric conversion, andphotoelectrons spread into the lateral direction due to diffusion.

On the other hand, as shown in FIG. 4, in the configuration, in which acondenser lens is disposed, the light is condensed on the vicinity ofthe center of the pixel in the photoelectric conversion layer 24 and,therefore, the diffusion current in the lateral direction is reduced.

FIG. 5 shows the results of simulation of this state.

As shown in FIG. 5, it is assumed here that the light is in the state ofbeing applied continuously and photoelectrons are yielded uniformly inthe photoelectric conversion layer 24 of one pixel. Then, estimation isconducted while the thickness of the photoelectric conversion layer 24(conductive layer 22) is assumed to be 0.5 μm, the pixel size is assumedto be 1.5 μm, the resistivity of the photoelectric conversion layer 24is assumed to be 0.2 Ωm, and the reading voltage is assumed to be 5 V.Regarding the current distribution, the distribution just above thefirst electrode 21 is estimated.

Moreover, the NA of the condenser lens 33 is assumed to be 0.6, and thestate, in which photoelectric conversion occurs intensely at the centerof the pixel (light condensation state), is determined from the formulaof Bessel function of the Airy disc.

As is clear from these results, in the state, in which there is nocondenser lens 33, the current spreads to the outside of the pixel,whereas the current is gathered in the vicinity of the center by usingthe condenser lens 33 and, consequently, leakage current to the outsideof the pixel is reduced.

This refers to a reduction in color mixing and an improvement in colorreproducibility. In particular, in the case of an organic conductivelayer, it is not easy to etch the boundary region of the pixel by thetechnology, e.g., lithography, an RIE process, or the like. According tothe method by using the condenser lens 33, a process for separatingpixels from each other becomes unnecessary, and there is a costadvantage.

Explanation of Reading Circuit of Solid-State Imaging Device

FIG. 6 shows a reading circuit 51 of a signal.

In the above-described reading circuit 51, a diffusion layer of a resettransistor M1 and a gate electrode of an amplifying transistor M2 areconnected to a floating diffusion portion FD connected to aphotoelectric conversion portion 52. Furthermore, a selection transistorM3 sharing a diffusion layer of the amplifying transistor M2 isconnected. An output line is connected to a diffusion layer of thisselection transistor M3. In this regard, the above-describedphotoelectric conversion portion 51 is formed from the above-describedphotoelectric conversion layer 24, the first electrode 21, the plug 16,the pixel electrode 13, the charge accumulation layer 12, and the like,as described above with reference to FIG. 1.

In this manner, the process is made easy by producing the individualtransistors of the reading circuit 51, the charge accumulation layer 12,pixel electrode 13, and the like on the silicon substrate 11 (refer toFIG. 1 described above) in advance, and producing the above-describedstructure as a layer thereon.

Explanation of Band Diagram of Solid-State Imaging Device

FIG. 7 to FIG. 10 show band diagrams with respect to the above-describedsolid-state imaging device 1.

FIG. 7 and FIG. 9 show the case of zero bias, and FIG. 8 and FIG. 10show the case where a reverse bias is applied.

In FIG. 7 and FIG. 8, the first electrode 21, which is a metalelectrode, has a large work function, and the HOMO level (or the energylevel of the valence band) of the conductive layer 22 is close to theFermi level of the metal. For example, the case wherepoly2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) isused as the conductive layer 22 and aluminum (Al) is used as the firstelectrode 21, which is a metal electrode, corresponds to this.

In FIG. 9 and FIG. 10, the first electrode 21, which is a metalelectrode, has a small work function, and the Fermi level of the metalis higher than the HOMO level (or the energy level of the valence band)of the conductive layer 22. For example, the case where MEH-PPV is usedas the conductive layer 22 and lithium (Li) based material (for example,LiF) or calcium (Ca) is used as the first electrode 21, which is a metalelectrode, corresponds to this.

As shown in FIG. 8 described above, an electron passes from theconductive layer 22 to the first electrode 21 side by application of areverse bias voltage +V, but since the potential barrier of a holepresent on the first electrode 21 side is small, the hole moves from thefirst electrode 21 to the conductive layer 22 due to a tunnel effect atthe same time. As a result, a leakage current occurs.

On the other hand, as shown in FIG. 10, even when the reverse biasvoltage +V is applied, a leakage current is small because the potentialbarrier of a hole present on the first electrode 21 side is large.

Therefore, it is desirable that the first electrode 21, which is a metalelectrode, under (the side opposite to the light-incident side relativeto the photoelectric conversion layer 24) the photoelectric conversionlayer 24 is formed from a material having a work function smaller thanthat of the conductive layer 22.

In the case where the material is selected in consideration of theproperties, as described above, it becomes possible to suppress aleakage current and read merely signal intensity efficiently, so that animage having a high S/N ratio can be obtained.

2. Second Embodiment Second Example of Solid-State Imaging Device

A second example of the configuration of a solid-state imaging deviceaccording to a second embodiment of the present invention will bedescribed below.

This solid-state imaging device 2 corresponds to the above-describedsolid-state imaging device 1, in which at least one type of an inorganicphosphor, a light-emitting colorant, and an organic phosphor serving asa light-emitting material is introduced dispersing into thephotoelectric conversion layer 24 (conductive layer 22), so as to reducephoton shot noises.

Explanation of Photon Shot Noise

Initially, a photon shot noise will be described.

Since the photon is a Bose particle, overlapping of particles occurs,and in the continuous light, there are parts, in which photons aredense, and parts, in which photons are sparse (photon bunching effect).This causes an occurrence of temporal and spatial fluctuations in thenumber of incident photons. This is the origin of the photon shot noise.

This photon shot noise Nn follows the Poisson's distributionstatistically and satisfiesNn=√Nswhere the number of incident photons per unit time is assumed to be Ns.At this time, the SN ratio becomesNs/Nn=Ns/√Ns=√Ns.

Therefore, as the number of incident photons Ns decreases, the SN ratiodecreases theoretically.

On the other hand, the photon shot noise of the solid-state imagingdevice (image sensor) is determined on the basis of the spatialfluctuation. If the amplitude of the temporal fluctuation of each pixelis reduced, the spatial fluctuation can be reduced at the same time.

That is, as shown in FIG. 11, there is a difference in the number ofincident photons per unit time between a pixel 41 and a pixel 42 at eachof the time t₁ of the day and the time t₂ of the day.

At the time t₁ of the day,(the number of incident photons per unit time of the pixel 41)>(thenumber of incident photons per unit time of the pixel 42)holds. At the time t₂ of the day,(the number of incident photons per unit time of the pixel 42)>(thenumber of incident photons per unit time of the pixel 41)holds. This refers to that light and shade in the image at the time t₁of the day are reverse of those at the time t₂ of the day, and light andshade in the image of pixel 41 are reverse of those of the pixel 42.

Such a difference corresponds to a spatial fluctuation at each time ofthe day so as to become a sensor noise. Here, if it is provided that theamplitude of the spatial fluctuation is reduced as indicated by a brokenline shown in the drawing, this difference is reduced, and the spatialfluctuation, that is, noises of the sensor are reduced.

Configuration of Second Example of Solid-State Imaging Device

The second example of the configuration of the solid-state imagingdevice according to the second embodiment of the present invention willbe described with reference to a schematic configuration sectional viewshown in FIG. 12.

As shown in FIG. 12, for example, a p-type silicon substrate is used asa silicon substrate 11. A plurality of pixels are disposed on theabove-described silicon substrate 11. In the drawing, two pixels areshown as typical examples.

A charge accumulation layer 12 is disposed on the above-describedsilicon substrate 11 on a pixel basis. This charge accumulation layer 12is formed from, for example, an n-type impurity diffusion layer. Forexample, the silicon substrate 11 is doped with an n-type impurity,e.g., phosphorus (P) or arsenic (As), so as to form the chargeaccumulation layer 12.

Pixel electrode 13 is disposed on the above-described chargeaccumulation layer 12. Furthermore, a gate MOS 14 to read a signal fromthe charge accumulation layer 12 to a reading circuit (not shown in thedrawing) is disposed, on a pixel basis, on the above-described siliconsubstrate 11. In this gate MOS 14, a gate electrode 14-2 is disposed onthe silicon substrate 11 with a gate insulating film 14-1 therebetween.

An insulating film 15 covering the above-described pixel electrodes 13,the gate MOSs 14, and the like is disposed on the above-describedsilicon substrate 11. This insulating film 15 is formed from, forexample, a silicon oxide film. As a matter of course, the insulatingfilm 15 may be formed from an inorganic insulating film or an organicinsulating film other than the silicon oxide film.

Plugs 16 connected to the above-described pixel electrodes 13 aredisposed in the above-described insulating film 15. This plug 16 isformed from, for example, tungsten. As a matter of course, electricallyconductive materials other than tungsten can be used.

First electrodes 21 connected to the above-described plugs 16 aredisposed on the above-described insulating film 15. These firstelectrodes 21 are disposed separately on a pixel basis. This electrodeis formed from a transparent electrode material of, for example, indiumtin oxide (ITO), indium zinc oxide, or zinc oxide. Alternatively, thiselectrode is formed from a metal electrode of lithium fluoride (LiF),calcium, or the like. That is, it is preferable that the metal electrodeof the first electrode 21 has a work function smaller than the workfunction of a conductive layer 22 and the Fermi level of the metalelectrode of the first electrode 21 is higher than the HOMO level (orthe energy level of a valence band) of the conductive layer 22.

A photoelectric conversion layer 24 is disposed on the above-describedfirst electrodes 21. In this photoelectric conversion layer 24, narrowgap semiconductor quantum dots 23 and light-emitting members 26 aredispersed in the conductive layer 22.

The above-described narrow gap semiconductor quantum dot 23 has a bandgap of 1 eV or less and is formed in such a way that the particlediameter is, for example, 10 nm or less. Examples of materials thereforinclude a lead selenium compound (PbSe), a lead sulfur compound (PbS), alead tellurium compound (PbTe), a cadmium selenium compound (CdSe), acadmium tellurium compound (CdTe), an indium antimony compound (InSb),and an indium arsenic compound (InAs).

As for the above-described light-emitting member 26, at least one typeof an inorganic phosphor, a light-emitting colorant, and an organicphosphor is used. For example, the above-described inorganic phosphor iscomposed of a manganese-doped fluoride inorganic phosphor.

Furthermore, as for the above-described conductive layer 22, MEH-PPV isused.

A second electrode 25 is disposed on the above-described photoelectricconversion layer 24. This second electrode 25 is an electrode on thelight-incident side and, therefore, is formed from a transparentelectrode of, for example, indium tin oxide (ITO), indium zinc oxide, orzinc oxide, which has a light-transmitting property.

Moreover, color filter layers 31 are disposed on the above-describedsecond electrode 25. In this regard, a transparent insulating film (notshown in the drawing) may be disposed as a base material of the colorfilter layers 31.

In addition, a condenser lens 33 is disposed, on a pixel basis, on theabove-described color filter layer 31.

The solid-state imaging device 2 has the above-described configuration.

In the above-described solid-state imaging device 2, in order to levelthe temporal fluctuation in the number of photons, the light-emittingmembers 26 are introduced in the photoelectric conversion layer 24.

Consequently, as shown in FIG. 13, a function is performed in such a waythat absorption increases when the number of photons increases and adecrease in the number of photons is compensated by light emission ofthe light-emitting members 26 when the number of photons decreases, andleveling indicated by broken line is conducted.

In the above-described solid-state imaging device 2, for example, thenarrow gap semiconductor quantum dots 23 and the light-emitting members26 are mixed and introduced. Consequently, the number of photons isleveled through light emission and absorption, the photons can undergophotoelectric conversion, so that a high quantum efficiency can beobtained.

A specific extent of improvement of the SN ratio was estimated withrespect to a Green pixel having a pixel size of 1.1 μm. In this regard,the SN ratio here is defined as 20×log(Signal/Noise) in terms of dB.

As for the condition of the phosphor, in the case where light emissionwas conducted at an absorptance of 0.5 and a quantum efficiency of 0.3,the time constant of light emission was assumed to be 1/30 sec. In thiscase, the SN ratio became 36.3 dB from 32.9 dB and, therefore, wasimproved by 3.4 dB. Furthermore, in the case where light emission wasconducted at an absorptance of 0.5 and a quantum efficiency of 0.5, thetime constant of light emission was assumed to be 1/30 sec. In thiscase, the SN ratio became 38.6 dB from 32.9 dB and, therefore, wasimproved by 5.7 dB.

In addition, in the case where light emission was conducted at anabsorptance of 0.6 and a quantum efficiency of 1.0, the time constant oflight emission was assumed to be 1/30 sec. In this case, the SN ratiobecame 64.4 dB from 32.9 dB and, therefore, was improved by 31.5 dB.

The above-described estimation was premised on a Sin wave with afrequency of photon fluctuation of 15 Hz.

Furthermore, as for the other conditions, on the light source side, thecolor temperature was 3,200 K, and the brightness was 706 nit. On theimaging side, the image surface illuminance was 11.0 lx, the exposuretime was 1/30 sec, and the F value was 5.6. Moreover, an infrared-cutfilter and a color filter were disposed.

In this regard, as an example, FIG. 14 shows the results of simulationof changes over time in the case where the absorptance of the phosphorwas 0.6, the quantum efficiency was 1.0, and the time constant of lightemission was 1/30 sec. As is clear from FIG. 14, the amplitude offluctuation is reduced.

Consequently, the above-described solid-state imaging device 2 includesthe photoelectric conversion layer 24, in which narrow gap semiconductorquantum dots 23 are dispersed in the conductive layer 22 and, thereby,the avalanche multiplication can be effected by low voltage drive.Hence, there is an advantage that the sensitivity of even a fine pixelcan be enhanced through multiplication. Furthermore, at least one typeof an inorganic phosphor, a light-emitting colorant, and an organicphosphor is dispersed in the conductive layer 22, so that photon shotnoises are reduced.

Modified Example 1 of Second Example of Solid-State Imaging Device

In the case where the light-emitting members 26 are contained in thephotoelectric conversion layer 24 as in the above-described solid-stateimaging device 2, an afterimage may occur. As a result, an imagemovement may occur in the case of a moving subject or hand shaking. Thecase where a phosphor is used as the light-emitting member 26 will bedescribed below.

In this case, as shown in FIG. 15, this phenomenon can be reduced to aninsignificant level desirably by setting the time constant τ of lightemission of the phosphor within the exposure time t₁.

Here, the time constant τ of light emission refers to a time elapsedsince excitation light, which is a short pulse wave, enters at the time0 until the emission intensity I attenuates to 1/e, as shown in thedrawing. Here, e represents the Napier's constant or the base of thenatural logarithm.

It is desirable that the time constant τ of light emission of thephosphor is within the exposure time t₁. On the other hand, if the timeconstant is too short, the effect of reducing photon shot noises isreduced.

Therefore, it is optimum that the time constant of light emission is setat the maximum within an exposure time of a common camera of 1/15 sec to1/60 sec.

For example, a manganese (Mn)-doped fluoride based phosphor has a largetime constant of light emission, and some materials have time constantsof light emission on the order of 10 msec. For example, it is clear thatin the case where Ca₅(PO₄)₃F:Mn is used as the phosphor, the timeconstant τ of light emission is 14 msec and is close to an optimum time.

Up to this point, the case where the phosphor is used as thelight-emitting member 26 has been described mainly. However, lightemitting materials can exert the same effects. For example, alight-emitting colorant or an organic phosphor may be introduced in thesame manner.

As described above, the afterimage can be suppressed by specifying theindividual time constants of light emission of the light-emittingmembers 26, e.g., the inorganic phosphor, the light-emitting colorant,and the organic phosphor, to be shorter than the exposure time of theabove-described photoelectric conversion layer 24.

Modified Example 2 of Second Example of Solid-State Imaging Device

Furthermore, as shown in FIG. 16, it is desirable that theabove-described light-emitting members 26 in the solid-state imagingdevice 3 are dispersed in a manner described below. For example, thelight-emitting members 26, which are composed of the above-describedinorganic phosphor, the above-described light-emitting colorant, or theabove-described organic phosphor, in an amount larger than the amount ofthe above-described narrow gap semiconductor quantum dots 23 isdispersed at the center of the above-described conductive layer 22 inthe thickness direction. Moreover, the narrow gap semiconductor quantumdots 23 in an amount larger than the amount of the above-describedlight-emitting members 26 are dispersed on the above-described firstelectrode 21 side and the above-described second electrode 25 side ofthe above-described conductive layer 22.

The other configurations are the same as those of the solid-stateimaging device 1 described with reference to FIG. 1 described above.

That is, for example, a p-type silicon substrate is used as a siliconsubstrate 11. A plurality of pixels are disposed on the above-describedsilicon substrate 11. In the drawing, two pixels are shown as typicalexamples.

A charge accumulation layer 12 is disposed on the above-describedsilicon substrate 11 on a pixel basis. This charge accumulation layer 12is formed from, for example, an n-type impurity diffusion layer. Forexample, the silicon substrate 11 is doped with an n-type impurity,e.g., phosphorus (P) or arsenic (As), so as to form the chargeaccumulation layer 12.

Pixel electrode 13 is disposed on the above-described chargeaccumulation layer 12. Furthermore, a gate MOS 14 to read a signal fromthe charge accumulation layer 12 to a reading circuit (not shown in thedrawing) is disposed, on a pixel basis, on the above-described siliconsubstrate 11. In this gate MOS 14, a gate electrode 14-2 is disposed onthe silicon substrate 11 with a gate insulating film 14-1 therebetween.

An insulating film 15 covering the above-described pixel electrodes 13,the gate MOSs 14, and the like is disposed on the above-describedsilicon substrate 11. This insulating film 15 is formed from, forexample, a silicon oxide film. As a matter of course, the insulatingfilm 15 may be formed from an inorganic insulating film or an organicinsulating film other than the silicon oxide film.

Plugs 16 connected to the above-described pixel electrodes 13 aredisposed in the above-described insulating film 15. This plug 16 isformed from, for example, tungsten. As a matter of course, electricallyconductive materials other than tungsten can be used.

First electrodes 21 connected to the above-described plugs 16 aredisposed on the above-described insulating film 15. These firstelectrodes 21 are disposed separately on a pixel basis. This electrodeis formed from a transparent electrode material of, for example, indiumtin oxide (ITO), indium zinc oxide, or zinc oxide. Alternatively, thiselectrode is formed from a metal electrode of lithium fluoride (LiF),calcium, or the like. That is, it is preferable that the metal electrodeof the first electrode 21 has a work function smaller than the workfunction of a conductive layer 22 and the Fermi level of the metalelectrode of the first electrode 21 is higher than the HOMO level (orthe energy level of a valence band) of the conductive layer 22.

A photoelectric conversion layer 24 having the above-describedconfiguration is disposed on the above-described first electrodes 21. Inthis photoelectric conversion layer 24, narrow gap semiconductor quantumdots 23 and light-emitting members 26 are dispersed in the conductivelayer 22. The configuration of dispersion is as described above.

The above-described narrow gap semiconductor quantum dot 23 has a bandgap of 1 eV or less and is formed in such a way that the particlediameter is, for example, 10 nm or less. Examples of materials thereforinclude a lead selenium compound (PbSe), a lead sulfur compound (PbS), alead tellurium compound (PbTe), a cadmium selenium compound (CdSe), acadmium tellurium compound (CdTe), an indium antimony compound (InSb),and an indium arsenic compound (InAs).

As for the above-described light-emitting member 26, at least one typeof an inorganic phosphor, a light-emitting colorant, and an organicphosphor is used. For example, the above-described inorganic phosphor iscomposed of a manganese-doped fluoride inorganic phosphor.

Furthermore, as for the above-described conductive layer 22, MEH-PPV isused.

A second electrode 25 is disposed on the above-described photoelectricconversion layer 24. This second electrode 25 is an electrode on thelight-incident side and, therefore, is formed from a transparentelectrode of, for example, indium tin oxide (ITO), indium zinc oxide, orzinc oxide, which has a light-transmitting property.

Moreover, color filter layers 31 are disposed on the above-describedsecond electrode 25. In this regard, a transparent insulating film (notshown in the drawing) may be disposed as a base material of the colorfilter layers 31.

In addition, a condenser lens 33 is disposed, on a pixel basis, on theabove-described color filter layer 31.

The solid-state imaging device 3 has the above-described configuration.

Regarding the solid-state imaging device 3, since the light-emittingmembers 26 have the above-described configuration, the light emittedfrom the light-emitting members 26 is absorbed by the narrow gapsemiconductor quantum dots 23 efficiently and undergoes photoelectricconversion. Consequently, the avalanche multiplication is effected.Moreover, the same operation and effects as those of the above-describedsolid-state imaging device 1 are obtained.

Regarding the above-described solid-state imaging device 3, thelight-emitting members 26 are introduced into the conductive layer 22and, thereby, photon shot noises are reduced, while the photon shotnoises occur significantly due to a decrease in the number of incidentphotons per unit time because of a size reduction of the pixel, a lowilluminance condition, a high-speed imaging condition, or the like.Hence, it is possible that high S/N ratio image quality becomescompatible with high sensitivity through multiplication.

Furthermore, good image quality with a high S/N ratio can be providedeven in the state, in which the number of photons incident on one pixelis small and the proportion of photon shot noises is large for thereason that the pixel size is small, high-speed imaging is conducted,imaging is conducted in a dark place, or the like.

3. Third Embodiment First Example of Method for ManufacturingSolid-State Imaging Device

A first example of a method for manufacturing a solid-state imagingdevice according to a third embodiment of the present invention will bedescribed below.

For example, the solid-state imaging device 1 shown in FIG. 1 describedabove can be applied to a photodiode of a CMOS image sensor shown inFIG. 17. In this regard, the band diagram of the above-describedsolid-state imaging device 1 is as shown in FIG. 18.

The above-described solid-state imaging device 1 can be formed on thesilicon substrate 11 by common CMOS process steps, for example. Theexplanation will be made below with reference to FIG. 1 described above.

A p-type (100) silicon substrate is used as the above-described siliconsubstrate 11. Initially, the pixel transistors, the gate MOSs 14, inwhich a gate electrode 14-2 is disposed on the gate insulating film14-1, used for reading, and circuits (not shown in the drawing) oftransistors, electrodes, and the like of periphery circuits are formedon the above-described silicon substrate 11.

Thereafter, the charge accumulation layers 12 are disposed on theabove-described silicon substrate 11. This charge accumulation layer 12is formed from, for example, an n-type silicon layer through ionimplantation. In this ion implantation, an ion implantation region isdelimited by using a resist mask. This resist mask is removed after theion implantation.

Subsequently, the pixel electrodes 13 are formed on the above-describedcharge accumulation layers 12.

For example, Al electrodes are formed on the above-described chargeaccumulation layers 12 through evaporation. This process is executed bya common Si-LSI process. As a matter of course, besides aluminum, it isalso possible to form from a gold wiring material, a metal compoundwiring material, or the like used for semiconductor apparatuses.

Then, the insulating film 15 covering the above-described pixelelectrodes 13, the gate MOSs 14, and the like is formed on theabove-described silicon substrate 11. This insulating film 15 is formedfrom, for example, a silicon oxide film.

Next, the plugs 16 connected to the above-described pixel electrodes 13are formed in the above-described insulating film 15. This plug 16 isformed by forming a contact hole reaching the above-described pixelelectrode 13 in the above-described insulating film 15 and, thereafter,embedding a conductor into the resulting contact hole.

Subsequently, the first electrodes 21 connected to the above-describedplugs 16 are formed on the above-described insulating film 15.

For example, Al electrodes connected to the above-described plugs 16 areformed on the above-described insulating film 15 through evaporation.This process can be executed by the common Si-LSI process. In addition,lithium fluoride (LiF) is evaporated on the surfaces of theabove-described Al electrodes, so as to suppress a leakage current dueto holes.

Then, the photoelectric conversion layer 24 is formed on theabove-described first electrodes 21 by forming the conductive layer 22,in which narrow gap semiconductor quantum dots 23 are dispersed.

For example, the above-described photoelectric conversion layer 24 isformed as described below. Initially, lead selenium compound (PbSe)quantum dots are dispersed in the electrically conductive polymermaterial, MEH-PPV, by a chemical synthesis method in advance. A film ismade therefrom by a spin coating method, so as to form theabove-described photoelectric conversion layer 24.

As for the above-described narrow gap semiconductor quantum dots 23,besides the lead selenium compound (PbSe), quantum dots of narrow gapsemiconductors of a lead sulfur compound (PbS), a lead telluriumcompound (PbTe), a cadmium selenium compound (CdSe), a cadmium telluriumcompound (CdTe), an indium antimony compound (InSb), an indium arseniccompound (InAs), and the like can be used.

Next, the second electrode 25 is formed on the above-describedphotoelectric conversion layer 24.

For example, a film of indium tin oxide (ITO) is formed as a transparentelectrode film all over the above-described photoelectric conversionlayer 24. For example, a sputtering method is used for this filmformation. Furthermore, a metal wiring connected to the above-describedsecond electrode 25 is wired and grounded to prevent charging due toaccumulation of holes.

Moreover, in order to effect smooth movement of holes to the secondelectrode 25 side, an intermediate layer (not shown in the drawing) of,for example, PEDOT/PPS may be formed between the second electrode 25,which is an ITO transparent electrode, and the photoelectric conversionlayer 24 of MEH-PPV before the above-described second electrode 25 isformed. This film formation can be conducted through spin coating, as inthe above description. The above-described PEDOT/PPS is an abbreviationof poly(2,3-dihydrothieno(3,4-b)-1,4-dioxin/poly(styrenesulfonate).

In addition, the color filters 31 are formed on the above-describedsecond electrode 25 of the individual pixels. Furthermore, the condenserlens 33 serving as the uppermost layer of this device is formed, on apixel basis, on the above-described color filter 31 to increase thelight condensation efficiency and reduce color mixing.

The solid-state imaging device 1 is formed as described above.

In the above-described solid-state imaging device 1, a signal is read byapplying a reverse bias to the above-described photoelectric conversionlayer 24. FIG. 18 shows a band diagram in the case where, for example, areverse bias is applied up to 3 V.

As shown in FIG. 18, the signal can be read from a voltage of about 3 V,and an adequate signal based on avalanche multiplication can be read byan application of a reverse bias up to 8 V. It becomes possible to driveat such a low voltage.

Second Example of Method for Manufacturing Solid-State Imaging Device

A second example of the method for manufacturing the solid-state imagingdevice according to the third embodiment of the present invention willbe described below.

For example, the solid-state imaging device 1 shown in FIG. 1 describedabove can be applied to a photodiode of a CCD image sensor shown in FIG.19.

The above-described solid-state imaging device 1 can be formed on thesilicon substrate 11 by common CCD process steps, for example. Theexplanation will be made below with reference to FIG. 1 described above.

A p-type (100) silicon substrate is used as the above-described siliconsubstrate 11. Initially, circuits of transfer gates (corresponding tothe gate MOS 14), vertical transfer CCDs, and the like are formed on theabove-described silicon substrate 11.

Thereafter, the charge accumulation layers 12 are disposed on theabove-described silicon substrate 11. This charge accumulation layer 12is formed from, for example, an n-type silicon layer through ionimplantation. In this ion implantation, an ion implantation region isdelimited by using a resist mask. This resist mask is removed after theion implantation.

Subsequently, the pixel electrodes 13 are formed on the above-describedcharge accumulation layers 12.

For example, Al electrodes are formed on the above-described chargeaccumulation layers 12 through evaporation. This process is executed bya common Si-LSI process. As a matter of course, besides aluminum, it isalso possible to form from a gold wiring material, a metal compoundwiring material, or the like used for semiconductor apparatuses.

Then, the insulating film 15 covering the above-described pixelelectrodes 13, the gate MOSs 14, and the like is formed on theabove-described silicon substrate 11. This insulating film 15 is formedfrom, for example, a silicon oxide film.

Next, the plugs 16 connected to the above-described pixel electrodes 13are formed in the above-described insulating film 15. This plug 16 isformed by forming a contact hole reaching the above-described pixelelectrode 13 in the above-described insulating film 15 and, thereafter,embedding a conductor into the resulting contact hole.

Subsequently, the first electrodes 21 connected to the above-describedplugs 16 are formed on the above-described insulating film 15.

For example, Al electrodes connected to the above-described plugs 16 areformed on the above-described insulating film 15 through evaporation.This process can be executed by the common Si-LSI process. In addition,lithium fluoride (LiF) is evaporated on the surfaces of theabove-described Al electrodes, so as to suppress a leakage current dueto holes.

Then, the photoelectric conversion layer 24 is formed on theabove-described first electrodes 21 by forming the conductive layer 22,in which narrow gap semiconductor quantum dots 23 are dispersed.

For example, the above-described photoelectric conversion layer 24 isformed as described below. Initially, lead selenium compound (PbSe)quantum dots are dispersed into the electrically conductive polymermaterial, MEH-PPV, by a chemical synthesis method in advance. A film ismade therefrom by a spin coating method, so as to form theabove-described photoelectric conversion layer 24.

As for the above-described narrow gap semiconductor quantum dots 23,besides the lead selenium compound (PbSe), quantum dots of narrow gapsemiconductors of a lead sulfur compound (PbS), a lead telluriumcompound (PbTe), a cadmium selenium compound (CdSe), a cadmium telluriumcompound (CdTe), an indium antimony compound (InSb), an indium arseniccompound (InAs), and the like can be used.

Next, the second electrode 25 is formed on the above-describedphotoelectric conversion layer 24.

For example, a film of indium tin oxide (ITO) is formed as a transparentelectrode film all over the above-described photoelectric conversionlayer 24. For example, a sputtering method is used for this filmformation. Furthermore, a metal wiring connected to the above-describedsecond electrode 25 is wired and grounded to prevent charging due toaccumulation of holes.

Moreover, in order to effect smooth movement of holes to the secondelectrode 25 side, an intermediate layer (not shown in the drawing) of,for example, PEDOT/PPS may be formed between the second electrode 25,which is an ITO transparent electrode, and the photoelectric conversionlayer 24 of MEH-PPV before the above-described second electrode 25 isformed. This film formation can be conducted through spin coating, as inthe above description. The above-described PEDOT/PPS is an abbreviationof poly(2,3-dihydrothieno(3,4-b)-1,4-dioxin/poly(styrenesulfonate).

A photoelectric conversion portion is formed as described above.

In addition, the color filters 31 are formed on the above-describedsecond electrode 25 of the individual pixels. Furthermore, the condenserlens 33 serving as the uppermost layer of this device is formed, on apixel basis, on the above-described color filter layer 31 to increasethe light condensation efficiency and reduce color mixing.

The solid-state imaging device 1 is formed as described above.

In the above-described solid-state imaging device 1, a signal is read byapplying a reverse bias to the above-described photoelectric conversionlayer 24. FIG. 18 described above shows a band diagram in the casewhere, for example, a reverse bias is applied up to 3 V.

As shown in FIG. 18 described above, the signal can be read from avoltage of about 3 V, and an adequate signal based on avalanchemultiplication can be read by an application of a reverse bias up to 8V. It becomes possible to drive at such a low voltage.

Third Example of Method for Manufacturing Solid-State Imaging Device

A third example of the method for manufacturing the solid-state imagingdevice according to the third embodiment of the present invention willbe described below.

For example, the solid-state imaging device 2 shown in FIG. 12 describedabove can be applied to a photodiode of the CMOS image sensor shown inFIG. 17 described above. Furthermore, the band diagram of theabove-described solid-state imaging device 2 is the same as that shownin FIG. 18 described above.

The above-described solid-state imaging device 2 can be formed on thesilicon substrate 11 by common CMOS process steps, for example. Theexplanation will be made below with reference to FIG. 12 describedabove.

A p-type (100) silicon substrate is used as the above-described siliconsubstrate 11. Initially, the pixel transistors, the gate MOSs 14, inwhich a gate electrode 14-2 is disposed on the gate insulating film14-1, used for reading, and circuits (not shown in the drawing) oftransistors, electrodes, and the like of periphery circuits are formedon the above-described silicon substrate 11.

Thereafter, the charge accumulation layers 12 are disposed on theabove-described silicon substrate 11. This charge accumulation layer 12is formed from, for example, an n-type silicon layer through ionimplantation. In this ion implantation, an ion implantation region isdelimited by using a resist mask. This resist mask is removed after theion implantation.

Subsequently, the pixel electrodes 13 are formed on the above-describedcharge accumulation layers 12.

For example, Al electrodes are formed on the above-described chargeaccumulation layers 12 through evaporation. This process is executed bya common Si-LSI process. As a matter of course, besides aluminum, it isalso possible to form from a gold wiring material, a metal compoundwiring material, or the like used for semiconductor apparatuses.

Then, the insulating film 15 covering the above-described pixelelectrodes 13, the gate MOSs 14, and the like is formed on theabove-described silicon substrate 11. This insulating film 15 is formedfrom, for example, a silicon oxide film.

Next, the plugs 16 connected to the above-described pixel electrodes 13are formed in the above-described insulating film 15. This plug 16 isformed by forming a contact hole reaching the above-described pixelelectrode 13 in the above-described insulating film 15 and, thereafter,embedding a conductor into the resulting contact hole.

Subsequently, the first electrodes 21 connected to the above-describedplugs 16 are formed on the above-described insulating film 15.

For example, Al electrodes connected to the above-described plugs 16 areformed on the above-described insulating film 15 through evaporation.This process can be executed by the common Si-LSI process. In addition,lithium fluoride (LiF) is evaporated on the surfaces of theabove-described Al electrodes, so as to suppress a leakage current dueto holes.

Then, the photoelectric conversion layer 24 is formed on theabove-described first electrodes 21 by forming the conductive layer 22,in which narrow gap semiconductor quantum dots 23 and the light-emittingmembers 26 are dispersed.

For example, the above-described photoelectric conversion layer 24 isformed as described below. Initially, lead selenium compound (PbSe)quantum dots and a phosphor, Ca₅(PO₄)₃F:Mn, are dispersed in theelectrically conductive polymer material, MEH-PPV, by a chemicalsynthesis method in advance. A film is made therefrom by a spin coatingmethod, so as to form the above-described photoelectric conversion layer24. MEH-PPV is an abbreviation ofpoly2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene.

As for the above-described narrow gap semiconductor quantum dots 23,besides the lead selenium compound (PbSe), quantum dots of narrow gapsemiconductors of a lead sulfur compound (PbS), a lead telluriumcompound (PbTe), a cadmium selenium compound (CdSe), a cadmium telluriumcompound (CdTe), an indium antimony compound (InSb), an indium arseniccompound (InAs), and the like can be used.

As for the above-described light-emitting member 26, at least one typeof an inorganic phosphor, a light-emitting colorant, and an organicphosphor is used. For example, a manganese-doped fluoride inorganicphosphor is used as the above-described inorganic phosphor.

Next, the second electrode 25 is formed on the above-describedphotoelectric conversion layer 24.

For example, a film of indium tin oxide (ITO) is formed as a transparentelectrode film all over the above-described photoelectric conversionlayer 24. For example, a sputtering method is used for this filmformation. Furthermore, a metal wiring connected to the above-describedsecond electrode 25 is wired and grounded to prevent charging due toaccumulation of holes.

Moreover, in order to effect smooth movement of holes to the secondelectrode 25 side, an intermediate layer (not shown in the drawing) of,for example, PEDOT/PPS may be formed between the second electrode 25,which is an ITO transparent electrode, and the photoelectric conversionlayer 24 of MEH-PPV before the above-described second electrode 25 isformed. This film formation can be conducted through spin coating, as inthe above description. The above-described PEDOT/PPS is an abbreviationof poly(2,3-dihydrothieno(3,4-b)-1,4-dioxin/poly(styrenesulfonate).

In addition, the color filters 31 are formed on the above-describedsecond electrode 25 of the individual pixels. Furthermore, the condenserlens 33 serving as the uppermost layer of this device is formed, on apixel basis, on the above-described color filter layer 31 to increasethe light condensation efficiency and reduce color mixing.

The solid-state imaging device 2 is formed as described above.

In the above-described solid-state imaging device 2, a signal is read byapplying a reverse bias to the above-described photoelectric conversionlayer 24. In this regard, a band diagram similar to that shown in FIG.18 described above is exhibited.

Therefore, as shown in FIG. 18 described above, the signal can be readfrom a voltage of about 3 V, and an adequate signal based on avalanchemultiplication can be read by an application of a reverse bias up to 8V. It becomes possible to drive at such a low voltage. It was made clearthat photon shock noises were suppressed and, as a result, the imagequality of this solid-state imaging device 2 was high image quality witha high SN ratio and the sensitivity was high.

Fourth Example of Method for Manufacturing Solid-State Imaging Device

A fourth example of the method for manufacturing the solid-state imagingdevice according to the third embodiment of the present invention willbe described below.

For example, the solid-state imaging device 3 shown in FIG. 16 describedabove can be applied to a photodiode of the CMOS image sensor shown inFIG. 17 described above.

The above-described solid-state imaging device 3 can be formed on thesilicon substrate 11 by the common CMOS process steps, for example. Theexplanation will be made below with reference to FIG. 16 describedabove.

A p-type (100) silicon substrate is used as the above-described siliconsubstrate 11. Initially, the pixel transistors, the gate MOSs 14, inwhich a gate electrode 14-2 is disposed on the gate insulating film14-1, used for reading, and circuits (not shown in the drawing) oftransistors, electrodes, and the like of periphery circuits are formedon the above-described silicon substrate 11.

Thereafter, the charge accumulation layers 12 are disposed on theabove-described silicon substrate 11. This charge accumulation layer 12is formed from, for example, an n-type silicon layer through ionimplantation. In this ion implantation, an ion implantation region isdelimited by using a resist mask. This resist mask is removed after theion implantation.

Subsequently, the pixel electrodes 13 are formed on the above-describedcharge accumulation layers 12.

For example, Al electrodes are formed on the above-described chargeaccumulation layers 12 through evaporation. This process is executed bya common Si-LSI process. As a matter of course, besides aluminum, it isalso possible to form from a gold wiring material, a metal compoundwiring material, or the like used for semiconductor apparatuses.

Then, the insulating film 15 covering the above-described pixelelectrodes 13, the gate MOSs 14, and the like is formed on theabove-described silicon substrate 11. This insulating film 15 is formedfrom, for example, a silicon oxide film.

Next, the plugs 16 connected to the above-described pixel electrodes 13are formed in the above-described insulating film 15. This plug 16 isformed by forming a contact hole reaching the above-described pixelelectrode 13 in the above-described insulating film 15 and, thereafter,embedding a conductor into the resulting contact hole.

Subsequently, the first electrodes 21 connected to the above-describedplugs 16 are formed on the above-described insulating film 15.

For example, Al electrodes connected to the above-described plugs 16 areformed on the above-described insulating film 15 through evaporation.This process can be executed by the common Si-LSI process. In addition,lithium fluoride (LiF) is evaporated on the surfaces of theabove-described Al electrodes, so as to suppress a leakage current dueto holes.

Then, the photoelectric conversion layer 24 is formed on theabove-described first electrodes 21 by forming the conductive layer 22,in which narrow gap semiconductor quantum dots 23 and the light-emittingmembers 26 are dispersed.

For example, the above-described photoelectric conversion layer 24 isformed as described below. Initially, lead selenium compound (PbSe)quantum dots are dispersed in the electrically conductive polymermaterial, MEH-PPV, by a chemical synthesis method in advance. A film ismade therefrom by a spin coating method. Thereafter, the light-emittingmembers 26, for example, Ca₅(PO₄)₃F:Mn, which is a phosphor, aredispersed in the electrically conductive polymer material, MEH-PPV, anda film is made therefrom on the film containing PbSe. Furthermore, leadselenium compound (PbSe) quantum dots are dispersed in the electricallyconductive polymer material, MEH-PPV, by a chemical synthesis method inadvance, and a film is made therefrom by a spin coating method on theabove-described film containing the phosphor.

In this manner, films are made three times through spin coating and,thereby, the photoelectric conversion layer 24 is formed having athree-layer structure, in which a high proportion of light-emittingmember 26 is distributed in the vicinity of the center of the conductivelayer 22 in the thickness direction and on and under thereof, a highproportion of narrow gap semiconductor quantum dots 23 is distributed.

As for the above-described narrow gap semiconductor quantum dots 23,besides the lead selenium compound (PbSe), quantum dots of narrow gapsemiconductors of a lead sulfur compound (PbS), a lead telluriumcompound (PbTe), a cadmium selenium compound (CdSe), a cadmium telluriumcompound (CdTe), an indium antimony compound (InSb), an indium arseniccompound (InAs), and the like can be used.

Next, the second electrode 25 is formed on the above-describedphotoelectric conversion layer 24.

For example, a film of indium tin oxide (ITO) is formed as a transparentelectrode film all over the above-described photoelectric conversionlayer 24. For example, a sputtering method is used for this filmformation. Furthermore, a metal wiring connected to the above-describedsecond electrode 25 is wired and grounded to prevent charging due toaccumulation of holes.

Moreover, in order to effect smooth movement of holes to the secondelectrode 25 side, an intermediate layer (not shown in the drawing) of,for example, PEDOT/PPS may be formed between the second electrode 25,which is an ITO transparent electrode, and the photoelectric conversionlayer 24 of MEH-PPV before the above-described second electrode 25 isformed. This film formation can be conducted through spin coating, as inthe above description. The above-described PEDOT/PPS is an abbreviationof poly(2,3-dihydrothieno(3,4-b)-1,4-dioxin/poly(styrenesulfonate).

In addition, the color filters 31 are formed on the above-describedsecond electrode 25 of the individual pixels. Furthermore, the condenserlens 33 serving as the uppermost layer of this device is formed, on apixel basis, on the above-described color filter layer 31 to increasethe light condensation efficiency and reduce color mixing.

The solid-state imaging device 3 is formed as described above.

In the above-described solid-state imaging device 3, a signal is read byapplying a reverse bias to the above-described photoelectric conversionlayer 24. In this regard, a band diagram similar to that shown in FIG.18 described above is exhibited.

Therefore, as shown in FIG. 18 described above, the signal can be readfrom a voltage of about 3 V, and an adequate signal based on avalanchemultiplication can be read by an application of a reverse bias up to 8V. It becomes possible to drive at such a low voltage. It was made clearthat photon shock noises were suppressed and, as a result, the imagequality of this solid-state imaging device 3 was high image quality witha high SN ratio and the sensitivity was high.

As for the above-described conductive layer 22,poly2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) hasbeen described.

Examples of the above-described conductive layers 22, which exert thesame effects, include electrically conductive inorganic materials, e.g.,tin-antimony based oxide aqueous paints (produced by JEMCO, for example)and an aqueous dispersion of electrically conductive zinc oxide(produced by HAKUSUI TEC, for example). In addition to them,electrically conductive organic materials, e.g., polythiophene basedorganic electrically conductive polymer, are mentioned.

The photoelectric conversion layer 24 can be formed by dispersing theabove-described narrow gap semiconductor quantum dots 23 into theabove-described electrically conductive organic material or electricallyconductive inorganic material and, thereafter, applying the resultingsolution. As for the application of the above-described solution, notonly the above-described spin coating method, but also coating methods,e.g., bar coating and dipping, and printing methods, e.g., screenprinting and ink jet, can be used.

An example of the above-described dipping method will be described withreference to a schematic configuration diagram shown in FIG. 20.

As shown in FIG. 20, the silicon substrate 11, in which steps up to thefirst electrodes 21 (not shown in the drawing) have been completed inadvance, is dipped into the above-described solution 71 and the siliconsubstrate 11 is pulled upward, so that the solution is applied to thesurface of the silicon substrate 11. At this time, the thickness of thecoating film 81 (photoelectric conversion layer 24) can be controlled byadjusting the wettability of the surface through a nitrogen or oxygenplasma treatment or a hydrophilic chemical treatment of the surface ofthe silicon substrate 11 in advance or adjusting a pulling up speed ofthe silicon substrate 11. In general, the absorption coefficient of thenarrow gap semiconductor is about two orders of magnitude higher thanthe absorption coefficient of silicon and, therefore, if the thicknessof this photoelectric conversion layer 24 is 50 nm or more, a lightabsorption effect is exerted. Further desirably, in the case where thethickness is 500 nm or more, and 1 μm or less, an adequate lightabsorption effect is exerted.

Alternatively, as is explained with reference to FIG. 16 describedabove, the photoelectric conversion layer 24 may be formed while theconductive layer 22 containing the narrow gap semiconductor quantum dots23 and the conductive layer 22 containing the light-emitting members 26are separated. Moreover, a plurality of coating steps may be conductedrepeatedly in the formation of the individual films, so as to havedesired thicknesses.

Next, the proportions (percent by weight or volume ratio) of the narrowgap semiconductor quantum dots 23 and the light-emitting members 26 inthe conductive layer 22 and the types of the light-emitting members 26will be described.

The proportion of the narrow gap semiconductor quantum dots 23 in theconductive layer 22 of MEH-PPV is the same as the efficiency of a solarcell described in APPLIED PHYSICS LETTERS 86, 093103 (2005). Therefore,if MEH-PPV is specified to be 500 or more in terms of percent by weight,a multiplication effect is exerted. Further desirably, the proportion isspecified to be 97±2% to obtain a maximum efficiency. The same holds forthe other types of conductive layers.

In the case where the proportion of the light-emitting members 26 in theconductive layer 22 of MEH-PPV is 10 or more in terms of volume ratio inthe whole photoelectric conversion layer 24, the effect is exerted.Furthermore, 100 or more is desirable to exert adequate effects ofabsorption and light emission of the light-emitting members 26.

Here, it is desirable that the size of the light-emitting member 26 issmaller than or equal to the thickness of the photoelectric conversionlayer 24, that is, 1 μm or less. Moreover, nanosize particles of 50 nmor less are desirable to improve the dispersion characteristic in theconductive layer 22.

Examples of materials for the light-emitting member 26 include thefollowing materials besides manganese-doped fluoride based inorganicphosphors.

For example, a phosphor, in which a ZnS base material is doped with alight emission center, e.g., Ag, Al, or Cu, and a phosphor, in which aY₂O₂S base material is doped with a light emission center, e.g., Eu, areincluded. Furthermore, a phosphor, in which a (SrCaBaMg)₅(PO₄)₃Cl basematerial, a (Y,Gd)BO₃ base material, or a BaMgAl₁₀O₁₇ base material isdoped with a light emission center, e.g., Eu, is included.

Moreover, a phosphor, in which a LaPO₄ base material is doped with alight emission center, e.g., Ce or Tb, is included.

In addition, a phosphor, in which a Ca₁₀(PO₄)₆FCl base material is dopedwith a light emission center, e.g., Sb or Mn, is included.

Furthermore, a phosphor, in which a Zn₂SiO₄ base material is doped witha light emission center, e.g., Mn, is included.

Moreover, a phosphor, in which a Sr₄Al₁₄O₂₅ base material is doped witha light emission center, e.g., Eu or Dy, is included.

Next, a method for manufacturing the fine particles or the nanoparticlesof the narrow gap semiconductor quantum dots 23 and the light-emittingmembers 26 will be described below.

In the above description, the chemical synthesis method is described.However, other methods can be employed. For example, a plurality of or asingle compound raw material or a single element raw material isvaporized in a vacuum or in an inert gas, e.g., Ar, by a method ofresistance heating, electron beam irradiation heating, or the like andis deposited on the substrate, so that fine particles are formed. As amatter of course, the above-described plurality of or the singlecompound raw material or the single element raw material contains anelement constituting the above-described narrow gap semiconductorquantum dot 23 or the above-described light-emitting member 26. Thesefine particles are gathered and used for raw materials of the narrow gapsemiconductor quantum dot 23 and the light-emitting member 26.

Alternatively, a target of a material for the narrow gap semiconductorquantum dot 23 or the light-emitting member 26 is sublimated throughlaser abrasion or the like and is deposited on the substrate in the samemanner to form fine particles, followed by gathering.

In this regard, gathering is not necessarily conducted. Thenanoparticles or the fine particles of the narrow gap semiconductorquantum dot 23 and the light-emitting member 26 may be formed throughdirect evaporation on the conductive layer 22.

Furthermore, a conductive layer 22 is formed thereon again to make asandwich structure. In this case, the narrow gap semiconductor quantumdots 23 and the light-emitting members 26 are not necessarily dispersedin advance in the electrically conductive material for forming theconductive layer 22.

Alternatively, the nanoparticles or fine particles may be producedthrough pulverization. In this case, lumps of the raw material preparedin advance are worked into a desired size through pulverization with aball mill, a beads mill, or the like.

4. Fourth Embodiment One Example of Configuration of Imaging Apparatus

Next, an imaging apparatus according to an embodiment of the presentinvention will be described with reference to a block diagram shown inFIG. 21. This imaging apparatus includes the solid-state imaging deviceaccording to an embodiment of the present invention.

As shown in FIG. 21, an imaging apparatus 200 includes a solid-stateimaging device (not shown in the drawing) in an imaging portion 201. Animage-forming optical portion 202 to form an image is provided on thelight-condensing side of this imaging portion 201. Furthermore, theimaging portion 201 is connected to a signal processing portion 203including a drive circuit to drive the imaging portion 201, a signalprocessing circuit to process the signal, which is photoelectricallyconverted with the solid-state imaging device, into an image, and thelike. Moreover, the image signal processed with the above-describedsignal processing portion 203 can be stored in an image storage portion(not shown in the drawing). In such an imaging apparatus 200, as for theabove-described solid-state imaging device of the above-describedimaging portion 201, the solid-state imaging devices 1 to 3 described inthe above-described embodiment can be used.

Regarding the imaging apparatus 200 according to an embodiment of thepresent invention, since the solid-state imaging devices 1 to 3according to embodiments of the present invention are included, thesensitivity is enhanced and high-sensitivity imaging can be conducted.Consequently, deterioration of the image quality is suppressed, andimaging can be conducted with high sensitivity. Therefore, there is anadvantage that photographing can be conducted with high image qualityeven in a dark photographing environment, for example, in nightphotographing, or the like.

Incidentally, the imaging apparatus 200 according to an embodiment ofthe present invention is not limited to the above-describedconfiguration and can be applied to any imaging apparatus having aconfiguration including the solid-state imaging device.

The above-described solid-state imaging devices 1 to 3 may be in theform of one chip or in the form of a module, in which an imaging portionand a signal processing portion or an optical system are packagedcollectively and which has an imaging function. Here, the imagingapparatus refers to, for example, cameras and portable apparatuseshaving an imaging function. Furthermore, a term “imaging” is interpretedin a broad sense and includes not only capture of an image in usualpicture taking with a camera, but also detection of fingerprints and thelike.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-017470 filedin the Japan Patent Office on Jan. 29, 2009, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A solid-state imaging device comprising: asubstrate with a plurality of pixels; a plurality of charge accumulationregions in the substrate respectively corresponding to the pixels; foreach pixel, a pixel electrode on the substrate and over the respectivecharge accumulation region, the pixel electrode electrically coupled tothe respective charge accumulation region; for each pixel, a firstelectrode carried on the substrate and electrically connected to therespective pixel electrode, the first electrodes positioned in a commonlayer; a second electrode disposed opposed to the first electrodes; aphotoelectric conversion layer common to all of the pixels, which isdisposed between the first electrodes and the second electrode and inwhich narrow gap semiconductor quantum dots are dispersed in aconductive layer, the photoelectric conversion layer effective toconvert incident light into electrical charges suitable for generatingan image signal; and for each pixel, a color filter over the respectivecharge accumulation region, wherein, each pixel is comprised of arespective first electrode, a portion of the photoelectric conversionlayer, and the second electrode, charges generated by the photoelectricconversion layer based on light filtered by the color filters can bestored in the respective charge accumulation regions, the firstelectrodes are transparent electrodes and the second electrode is atransparent electrode or is a metal electrode, or the second electrodeis a transparent electrode and the first electrodes are transparentelectrodes or metal electrodes, an inorganic phosphor, a light-emittingcolorant, or an organic phosphor is dispersed in the conductive layer,the inorganic phosphor, the light-emitting colorant, or the organicphosphor in an amount larger than the amount of the narrow gapsemiconductor quantum dots is dispersed at the center of the conductivelayer in the thickness direction, and the narrow gap semiconductorquantum dots in an amount larger than the amount of the inorganicphosphor, the light-emitting colorant, or the organic phosphor aredispersed on the first electrode side and the second electrode side ofthe conductive layer.
 2. The solid-state imaging device according toclaim 1, wherein the narrow gap semiconductor quantum dots have a bandgap of 1 eV or less.
 3. The solid-state imaging device according toclaim 1, wherein the narrow gap semiconductor quantum dots are selectedfrom a lead selenium compound, a lead sulfur compound, a lead telluriumcompound, a cadmium selenium compound, a cadmium tellurium compound, anindium antimony compound, and an indium arsenic compound.
 4. Thesolid-state imaging device according to claim 1, wherein the conductivelayer comprisespoly2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene.
 5. Thesolid-state imaging device according to claim 1, wherein: the firstelectrodes are metal electrodes, the metal electrodes have a workfunction smaller than the work function of the conductive layer, and theFermi level of the metal electrodes is higher than the HOMO level of theconductive layer or the energy level of the valence band.
 6. Thesolid-state imaging device according to claim 5, wherein: the metalelectrodes are made of lithium fluoride or calcium, and the transparentelectrode is made of indium tin oxide.
 7. The solid-state imaging deviceaccording to claim 1, wherein each pixel has a condenser lens that isdisposed on the light-incident side of the pixel.
 8. The solid-stateimaging device according to claim 1, wherein the inorganic phosphorcomprises manganese-doped fluoride inorganic phosphor.
 9. Thesolid-state imaging device according to claim 1, wherein the individualtime constant of the inorganic phosphor, the light-emitting colorant, orthe organic phosphor is smaller than the exposure time of thephotoelectric conversion layer.
 10. The solid-state imaging device ofclaim 1, wherein: the first electrodes have a work function smaller thanthat of the conductive layer; and the first electrodes have a Fermilevel higher than a valance band energy level of the conductive layer.11. A solid-state imaging device comprising: a first electrode; a secondelectrode disposed opposed to the first electrode; and a photoelectricconversion layer, which is disposed between the first electrode and thesecond electrode and in which narrow gap semiconductor quantum dots aredispersed in a conductive layer, wherein, one electrode of the firstelectrode and the second electrode is a transparent electrode and theother electrode is a metal electrode or a transparent electrode, aninorganic phosphor, a light-emitting colorant, or an organic phosphor isdispersed in the conductive layer, the inorganic phosphor, thelight-emitting colorant, or the organic phosphor in an amount largerthan the amount of the narrow gap semiconductor quantum dots isdispersed at the center of the conductive layer in the thicknessdirection, and the narrow gap semiconductor quantum dots in an amountlarger than the amount of the inorganic phosphor, the light-emittingcolorant, or the organic phosphor are dispersed on the first electrodeside and the second electrode side of the conductive layer.
 12. A methodfor manufacturing a solid-state imaging device, the method comprisingthe steps of: forming a charge accumulation layer on a siliconsubstrate; forming a pixel electrode on the charge accumulation layer;forming an insulating film covering the pixel electrode; forming a plug,which is connected to the pixel electrode, in the insulating film;forming a first electrode, which is connected to the plug, on theinsulating film; forming a conductive layer, in which (1) narrow gapsemiconductor quantum dots and (2) an inorganic phosphor, alight-emitting colorant, or an organic phosphor is dispersed in theconductive layer on the first electrode, so as to form a photoelectricconversion layer; and forming a second electrode on the photoelectricconversion layer, wherein, one electrode of the first electrode and thesecond electrode is a transparent electrode and the other electrode is ametal electrode or a transparent electrode, the inorganic phosphor, thelight-emitting colorant, or the organic phosphor in an amount largerthan the amount of the narrow gap semiconductor quantum dots isdispersed at the center of the conductive layer in the thicknessdirection, and the narrow gap semiconductor quantum dots in an amountlarger than the amount of the inorganic phosphor, the light-emittingcolorant, or the organic phosphor are dispersed on the first electrodeside and the second electrode side of the conductive layer.
 13. Animaging apparatus comprising: a light-condensing portion to condenseincident light; an imaging portion including a solid-state imagingdevice to receive and photoelectrically convert the light condensed withthe light-condensing portion; and a signal processing portion to processthe signal subjected to the photoelectrical conversion, wherein, thesolid-state imaging device includes (a) a substrate with a plurality ofpixels; (b) a plurality of charge accumulation regions in the substraterespectively corresponding to the pixels; (c) for each pixel, a pixelelectrode on the substrate and over the respective charge accumulationregion, the pixel electrode electrically coupled to the respectivecharge accumulation region; (d) for each pixel, a first electrodecarried on the substrate and electrically connected to the respectivepixel electrode, the first electrodes positioned in a common layer; (e)a second electrode disposed opposed to the first electrodes; (f) aphotoelectric conversion layer common to all of the pixels, which isdisposed between the first electrodes and the second electrode and inwhich narrow gap semiconductor quantum dots are dispersed in aconductive layer, the photoelectric conversion layer effective toconvert incident light into electrical charges suitable for generatingan image signal; and (g) for each pixel, a color filter over therespective charge accumulation region, each pixel is comprised of arespective first electrode, a portion of the photoelectric conversionlayer, and the second electrode, charges generated by the photoelectricconversion layer based on light filtered by the color filters can bestored in the respective charge accumulation regions, the firstelectrodes are transparent electrodes and the second electrode is atransparent electrode or is a metal electrode, or the second electrodeis a transparent electrode and the first electrodes are transparentelectrodes or metal electrodes, an inorganic phosphor, a light-emittingcolorant, or an organic phosphor is dispersed in the conductive layer,the inorganic phosphor, the light-emitting colorant, or the organicphosphor in an amount larger than the amount of the narrow gapsemiconductor quantum dots is dispersed at the center of the conductivelayer in the thickness direction, and the narrow gap semiconductorquantum dots in an amount larger than the amount of the inorganicphosphor, the light-emitting colorant, or the organic phosphor aredispersed on the first electrode side and the second electrode side ofthe conductive layer.
 14. The solid-state imaging device of claim 13,wherein: the first electrodes have a work function smaller than that ofthe conductive layer; and the first electrodes have a Fermi level higherthan a valance band energy level of the conductive layer.